Travel to The Eye of Dartain and collect the book The Art of Spellshifting. The book is on a desk at ( 1805, 0, 4304 ) Copy/waypoint 1805, 0, 4304. (It has a star on the cover.)
You are instructed to check on Apprentice Tam, who has not yet returned.
Head into the Vermin Caves at ( 1458, -120, 3064 ) Copy/waypoint 1458, -120, 3064 and "Inspect" Apprentice Tam's body at ( 1255, -166, 3295 ) Copy/waypoint 1255, -166, 3295. (Inspecting Tam's body will not break any Invis. spell)
Collect 6 Twilight Blooms from Toxxulia Forest. These are around the area where the feral bruisers, Toxxulia savages and the bristlevine abhorrences roam. Some locs include:
Once again, travel to the Vermin Caves and find a "luminescent location" with "arcane infused waters" and saturate your new Jewel of the Underfoot.
The update is at ( 1293, -249, 3241 ) Copy/waypoint 1293, -249, 3241 at the bottom of the waterfall. Right click the luminescent item on the ground near the bottom of the pool. (This breaks invis.)